10 Questions You Should to Know about Roughness Gauge Manufacturer

In a previous life I worked for a German manufacture of surface roughness measuring equipment. One of my first jobs out of college was working on an optical roughness gauge.

Basically we fired a spot of light onto the surface and measured the scatter of the reflected light: A mirror reflected the light back as a spot, whereas a rough surface scattered the light across a diode array. It never really worked though. The resulting measured parameter couldn't be traced back to a standardized parameter such as Ra or Rz. Oil or other surface contamination was also a big issue.

Another method we used with good success was a laser from a CD (which was cutting edge technology at the time). The laser traced the surface, and the electronics that keep the laser focused on the CD surface told us the height of the surface if we traced the laser using a very accurate linear datum. The surface profile could be measured using the same parameters as a stylus based instrument. This system was used a lot in the semiconductor industry.

Another technique that worked in the lab was to scan a laser over the surface in a plane. The plane intersected the surface at 45 degrees. When you looked at the surface from 90 degrees (from the top) the laser traced a line that approximated the vertical surface profile. That one never got out of the lab!

But mostly our customers back then used a good old fashioned diamond stylus to trace a profile. I remember working on a probe with a very long reach to get inside the infamous o-ring grooves that brought down the Challenger shuttle. We could measure them easily but I'm not sure if our solution was ever used.

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NPL do a pretty good guide :-
The measurement of surface texture using stylus instruments.
Author(s):
Leach, R K
Source:Measurement Good Practice Guide No. 37

Goole search should pull up a direct download, "NPL UK Guide no 37" ought to work, or you can go to the right page on the NPL site, register and download that way.
NPL guides index is at

I had a Laser Talysurf in the lab for several years. I learned to drive it OK but franky never really felt I understood what was going on under the hood.

Clive

If its a porous surface, such as an oilite bush, odds are the roughness profile will be somewhat skewed which can upset the calculations in the instrument giving invalid results from simple measurements. Anything reasonably capable will have adjustments to sort this out but you do need to know what you are doing and understand what is going on. Simply trying to follow the manual painting by numbers fashion probably won't work. For simple instruments a larger stylus radii can be the factory solution. I belive this used to be the case with the old hand held Taylor Hobson instruments (late 's early 's vintage ??).NPL do a pretty good guide :-The measurement of surface texture using stylus instruments.Author(s):Leach, R KSource:Measurement Good Practice Guide No. 37Goole search should pull up a direct download, "NPL UK Guide no 37" ought to work, or you can go to the right page on the NPL site, register and download that way.NPL guides index is at Guides by number : Guides : Publications : National Physical Laboratory guide. All the ones I've used have been pretty good from the naming of names and scene setting point of view. Very handy when a more complete text drives you straight into the swamp of confusion.I had a Laser Talysurf in the lab for several years. I learned to drive it OK but franky never really felt I understood what was going on under the hood.Clive

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